Production of ethanol by microorganisms provides an alternative energy source to fossil fuels and is therefore an important area of current research. Zymomonas mobilis is a natural ethanologen that can be used for commercial production of ethanol. However, Z. mobilis does not naturally utilize xylose, which is the major pentose in hydrolyzed lignocellulosic materials. It is desirable for an ethanologen to utilize xylose, to make full use of the carbohydrate substrates in lignocellulosic biomass hydrolysate.
Zymomonas mobilis and other bacterial ethanologens which do not naturally utilize xylose may be genetically engineered for xylose utilization by introduction of genes encoding 1) xylose isomerase, which catalyses the conversion of xylose to xylulose; 2) xylulokinase, which phosphorylates xylulose to form xylulose 5-phosphate; 3) transketolase; and 4) transaldolase. There has been success in engineering Z. mobilis strains for xylose metabolism (U.S. Pat. No. 5,514,583, U.S. Pat. No. 5,712,133, U.S. Pat. No. 6,566,107, U.S. Pat. No. 5,726,053, Feldmann et al. (1992) Appl Microbiol Biotechnol 38: 354-361, Zhang et al. (1995) Science 267:240-243), as well as a Zymobacter palmae strain (Yanase et al. (2007) Appl. Environ. Mirobiol. 73:2592-2599). However, typically the engineered strains do not grow and produce ethanol as well on xylose as on glucose.
For this engineering, genes encoding the heterologous proteins for xylose metabolism have been expressed from promoters that are active in Z. mobilis cells, typically the promoter of the Z. mobilis glyceraldehyde-3-phosphate dehydrogenase gene or the promoter of the Z. mobilis enolase gene. Strains engineered for xylose utilization have been adapted by serial passage on xylose medium, resulting in strains with improved xylose utilization as described in U.S. Pat. No. 7,223,575 and U.S. Pat. No. 7,741,119. U.S. Pat. No. 7,989,206 and U.S. Pat. No. 7,998,722 disclose Z. mobilis glyceraldehyde-3-phosphate dehydrogenase gene promoters with improved activities and their use for expressing xylose isomerase for xylose utilization in Zymomonas. 
There remains a need for additional strong promoters that may be used in genetic engineering of Zymomonas, and other bacterial ethanologens to express genes that confer improved xylose utilization. The promoters may be used for expression of other genes as well.